JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
  <div>
  </div>
  <h2>I'm an h2</h2>
  <div>
    <span>I'm span 1</span>
    <span>I'm span 2</span>
    <span>I'm span 3</span>
  </div>
</div>
<div class="container">
  <div>
    <span>I'm span 1</span>
    <span>I'm span 2</span>
    <span>I'm span 3</span>
  </div>
  <h2>I'm an h2</h2>
  <div>
    <span>I'm span 4</span>
    <span>I'm span 5</span>
    <span>I'm span 6</span>
  </div>
</div>
<div class="container">
  <div>
    <span>I'm span 1</span>
    <span>I'm span 2</span>
  </div>
  <h2>I'm an h2</h2>
  <div>
    <span>I'm span 3</span>
  </div>
</div>
<div class="container">
  <div>
    <span>I'm a span</span>
    <span>I'm a span</span>
  </div>
  <div>

  </div>
  <h2>
    I'm an h2
  </h2>
</div>
<div class="container">
  <div>
    <span>I'm a span</span>
    <span>I'm a span</span>
  </div>
  <h2>
    I'm an h2
  </h2>
</div>
<div class="container">
  <h2 class="diff-order">
    I'm an h2
  </h2>
  <div class="diff-order">
    <span>I'm a span</span>
    <span>I'm a span</span>
  </div>
  <div class="diff-order">
    <span>I'm a span</span>
    <span>I'm a span</span>
  </div>
</div>
<p><span>TRUE CENTER</span></p>

CSS

.container {
  display: flex;
}
.container > * {
  flex: 1;  /* KEY RULE */
  border: 1px dashed red;
}
h2 { 
  text-align: center;
  margin: 0;
}
.container > div {
  display: flex;
}
.diff-order {
  order: 2
}
.diff-order:not(h2) {
  order: 1;
}
p { text-align: center;}
p > span { background-color: aqua; padding: 5px; }